From a perspective of preserving the environment, wind turbine generators using wind power in a form of renewable energy are becoming popular. A wind turbine generator is normally provided with a rotor having a plurality of blades mounted to a hub. The rotor is installed to a nacelle arranged on a tower installed onshore or offshore in a standing manner. In the wind turbine generator, the rotor is rotated upon receiving wind on the blades and the rotation of the rotor is increased by a speed increaser and transmitted to a generator housed in the nacelle and finally power is generated in the generator.
The speed increaser provided between the rotor and the generator may be, for instance, a gear type having planetary gears or a hydraulic transmission type having a hydraulic pump and a hydraulic motor.
The wind turbine generator is formed by blades, a speed increaser of the gear type, the hydraulic transmission type, etc., a hub, a nacelle, bearings such as a main shaft bearing and a yaw bearing, a variety of components such as a tower. When these parts deteriorate or break down, the wind turbine generator is forced to be shut down the operation. Therefore, it is important to prevent unexpected shutdown of the wind turbine generator by monitoring conditions of the parts of the wind turbine generator.
Patent Literature 1 describes an operation method of the wind turbine generator. According to the operation method, the remaining lifetime of the component is estimated by a condition monitoring system, CMS, and the output (power production) is controlled to adjust the remaining lifetime to a desired remaining lifetime. For instance, if it is estimated that the remaining lifetime of the component won't last till the coming scheduled maintenance, the output is lowered so as to prolong the remaining lifetime of the component to reach the time of the coming scheduled maintenance. As a result, not only that unplanned shutdown due to the failed component is prevented but also that unscheduled maintenance is performed less frequently. This results in increased income obtained from such wind turbine generator.